Even if you did happen to take a bullet, your chances of making it out alive are still in the balance. It’s almost impossible to imagine what it must be like to have been shot and be wounded, but there are critical steps you can take to stay alive until medical help arrives on the scene.
Of course, all of this would also be totally unnecessary if everyone was able to freely carry. No one would bother trying to shoot up a school if they knew at least 1/2 of the people there could and would shoot back.
And have you seen most teachers? Yeah, they're going to go hand to hand with a shooter and take them out. Sure. Just another example of GRRRRLLL power trying to be realistic.